This is a tentative fix forhttps://issues.jenkins.io/browse/JENKINS-76298

In a nutshell, builds that start without parameter values callAbstractScriptableParameter#getDefaultParameterValue for everyAbstractScriptableParameter in the job parameters once per everyparams read, which causes the same script to be executed over and over just to render the same value. In my case this is making first builds of multibranch pipeline jobs extremely slow once users push their new branches, as that build starts without parameters and my pipeline does a lot ofparams access at the first stage, which triggers this situation.

Testing done

You can reproduce the problem and validate my fix by following these steps:

1. Start a local Jenkins instance
2. Create a Pipeline: New Item -> Pipeline, doesn't need to be multibranch.
3. Definition: Pipeline script, and use this repro pipeline:

properties([    parameters([        string(name:"STRING_PARAM",defaultValue:"default",description:"A string parameter"),        [$class:'ChoiceParameter',choiceType:'PT_CHECKBOX',description:"PARAM_1",name:"PARAM_1",script: [               $class:'GroovyScript',script: [classpath: [],sandbox:true,script:"""                   Thread.sleep(2_000)                   return ['1']"""               ]           ]        ],        [$class:'ChoiceParameter',choiceType:'PT_CHECKBOX',description:"PARAM_2",name:"PARAM_2",script: [               $class:'GroovyScript',script: [classpath: [],sandbox:true,script:"""                   Thread.sleep(2_000)                   return ['2']"""               ]           ]        ],        [$class:'ChoiceParameter',choiceType:'PT_CHECKBOX',description:"PARAM_3",name:"PARAM_3",script: [               $class:'GroovyScript',script: [classpath: [],sandbox:true,script:"""                   Thread.sleep(2_000)                   return ['3']"""               ]           ]        ]    ])])stage('Test') {    echo"- STRING_PARAM -"    echo params.STRING_PARAM    echo params.STRING_PARAM    echo params.STRING_PARAM    echo"- PARAM_1 -"    echo params.PARAM_1    echo params.PARAM_1    echo params.PARAM_1    echo"- PARAM_2 -"    echo params.PARAM_2    echo params.PARAM_2    echo params.PARAM_2    echo"- PARAM_3 -"    echo params.PARAM_3    echo params.PARAM_3    echo params.PARAM_3}properties([parameters()])

4. Run it once, go into the console and make sure you accept thestaticMethod java.lang.Thread sleep long signature or else the scripts won't actually be running.
5. Now run it again, and notice how the pipeline takes 72 seconds to finish. This is the number of parameter accesses (12) multiplied by the total sleep time of the scripts (6 seconds), which proves that every access toparams is retriggering all the scripts in series while calculating the default value.
6. Install my version of the plugin and rerun the pipeline. You might need to accept thestaticMethod java.lang.Thread sleep long signature again if you restart Jenkins and don't have that persisted.
7. It will now take just 6 seconds, as the first access toparams will calculate all the default values, but further accesses will use the cached values.

Here's a screenshot before/after (middle hidden build is where I needed to accept the signature again):

Submitter checklist

• Make sure you are opening from atopic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed